Using a mandoline, Y peeler or vegetable peeler, slice zucchini into 1/8 inch thick slices lengthwise. To do so, trim both ends of zucchini and remove the first slice. Then slice it on a mandoline or hold one end in one hand and slice off the strips by holding a peeler in another hand. Be sure they are thin and uniform as possible, so we can roll them.
Preheat oven to 375 degrees F. In a large bowl, add chicken, ricotta cheese, Parmesan cheese, egg and 3/4 cup marinara sauce. Mix well.
Spread 1/2 cup marinara sauce at the bottom of 9x13 baking dish. Lay zucchini slice flat on a counter, spread 1 tablespoon of ricotta filling, leaving the end empty, and roll. Place in prepared baking dish. Proceed with remaining 23 roll ups, tucking them tightly with a seam side close to each other, so they don't unroll. After re-arrange them a bit in 4 rows of 8 roll ups each.
Top with remaining marinara sauce and sprinkle with mozzarella cheese. Bake uncovered for 25 minutes or until cheese has melted and sauce is bubbling.
Remove rolls from the oven, cover and let stand for 10 minutes. Serve hot.
Notes
Store: Refrigerate in an airtight container for up to 5 days. I would be hesitant to freeze it as squash consists of 90% water & isn’t a good vegetable to freeze and thaw. You can try!